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Author Topic: General Questions About Air Lines/Fittings  (Read 5683 times)
Depewtee
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« on: November 13, 2009, 04:52:34 AM »

HI All!

I am in the process of building ramps so I can "officially and safely" get under my bus for the first time.  I am building them using treated 2"x10# pine lumber.  There will be 17 boards on either ramp secured together with 1/2" galvanized threaded rods. I cut all of the wood last weekend and will drill and fasten them together this weekend.  I will heed all of the advice on wheel chocking and blocking the bus for added safety.  

My first order of business will be to inspect the air lines feeding the rear air bags.  On my recent (and first trip) two weekends ago I noticed the rear air bags would not air up.  I managed to get the bus into a position where I could crawl under and take a look and I found a pinched air line going to the right side bags (it was actually folded over/pinched like a garden hose gets sometimes).  I was able to straighten the hose and the bags aired up, but later on the return trip I experienced the same problem, although I did have some air left in the bags.  

Also, at this same time I noticed the source of one of my biggest air leaks (one of many).  There is a valve feeding air to the rear brakes that looks like it had a diaphragm on the bottom of it at one time.  The diaphragm is no longer there and the air comes out at a pretty good pace (you can hear standing beside the bus).  The valve is mounted above and in front of the drive axle and is secured to the back of the rear bay (I think - I was not in a position to inspect it closely, so it might have been mounted to something else, but it was in that general area).  I noticed on this trip that my brakes did not seem to be as efficient as before.  It felt like I was running with just the front brakes.  Is that a likely scenario?  At the time I choked it up to the first time driving the bus with a full tank of fuel, fuel tank of water, fully loaded for an extended weekend, and with three of my buddies on board - one of which tips the scales at over 400 lbs. (he is a big person at over 6'6" tall).

As I begin to replace lines and fittings what do I need to watch out for (tricks of the trade).  I know in plumbing applications I use Teflon tape on my fittings - is this a good idea or a bad idea in a bus application?  Is there one type of air line better than another?  I have a NAPA store close by, but I do not have ready access to any big truck parts suppliers.  Any advice would be appreciated.

By the way, the bus is a 1984 TMC (aka MCI) MC-9.  The previous owner had installed a series of valves and switches in the curb-side rear bay to allow the bus to be leveled using the rear air bags. I am thinking of removing this setup entirely as I have twice had problems with it not allowing the rear bags to air up (not counting my current problem).

Brian
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Brian Shonk
Fort Walton Beach, FL (Florida Panhandle)
1981 Prevost LeMirage Liberty Coach
1984 TMC MC-9
John316
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« Reply #1 on: November 13, 2009, 05:02:29 AM »

Brian,

First off, from your description, sounds like you have a hole in one of your brake can diaphragms. Ours did something similar when it had a little hole in there. So you need to service your brakes.

I use True-Blu, on all of my fittings. That has worked very well.

I will see who else responds, because I have to run right now. If nobody else responds, I will make a longer post.

God bless,

John
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MCI 1995 DL3. DD S60 with a Allison B500.
desi arnaz
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« Reply #2 on: November 13, 2009, 05:10:24 AM »

go to a fastenall store, they have the best 700 psi fittings at fair prices.and they have more selection than any other store in town.
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robertglines1
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« Reply #3 on: November 13, 2009, 05:21:00 AM »

soapy water time once you get the leaks you can hear repaired.Use soapy water to check your repairs and look for other problems..The regulator that is mounted in the rear wheel area should be replaced take it off should be available locally if not go to MCI web page and parts they are usually very reasonable and deliver to your door..down load a air(pneumatic)digram that will help you follow how the air is suppose to go..air lines are color coded.....use air lines that meet DOT requirements...no kinks...fasten air lines down to prevent rubbing against other parts(makes holes)..get your feet wet once you get into it is fairly simple..If your primary air is not getting high enough you 2nd system (accessory)will not have air to operate properly.
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Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana
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« Reply #4 on: November 13, 2009, 05:24:28 AM »

Truck stops will usually have air lines and fittings
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Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana
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« Reply #5 on: November 13, 2009, 05:30:27 AM »

I use gas rated pipe thread compound on all fittings, as a rule.  It seems to work fine, but I don't know the rules for air brake systems.  I have not changed any fittings or valves on the brake system yet.

I'm going to come out and say something you might find offensive, but I have a problem with something you said.  You said (or strongly implied) that you drove your bus on a trip with a brake system that you knew was leaking badly and you felt was performing improperly.  You noticed a problem, which could have been a failure of the rear brake valve, which controls the majority of the braking action of the bus, or the rear quick release valve was venting indicating a failed brake can diaphragm, and you went out anyway.  The bus should have been parked until it was fixed, there is no excuse for driving a bus that has a known faulty braking system.  An audible leak in the braking system is a DOT downcheck.

With that said, if you are a novice at repairing and maintaining air brake systems, maybe a good course of action is to have it inspected by a licensed air-brake technician, get it up to snuff and in good working order, then ease into the ongoing maintenance as you go along.  Air brake systems are reasonably complex, although based on simple mechanical devices, and you need to have a thorough understanding of the entire system to really understand what is going on at times.  It's a lot easier to start with something you know is good and work from there.

I apologize if you think I'm being unduly harsh.  I think that amateurs maintaining commercial air brake systems is very achievable, but we need to maintain the same standards for safety as the commercial operators do.  Their rules and practices evolved for a reason, and we  need to respect that experience.  If I mis-interpreted your post, I again apologize.


Brian
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Depewtee
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« Reply #6 on: November 13, 2009, 05:45:52 AM »

Brian -

No offense taken.  It is in retrospect that I realize there might be a connection between perceived reduced braking capability and the leaky valve.  I did not hear and/or find the leaky valve until I climbed under the bus to inspect the air bag problem.  This was the first time the bus was fully loaded, so the braking capability for that condition may be normal - I never had a problem stopping; however, I could tell there was extra weight on the bus.  Thanks for all of the replies so far.  Please chime in with information as you deem appropriate as I will be beginning this project this weekend.

Brian Smiley
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Brian Shonk
Fort Walton Beach, FL (Florida Panhandle)
1981 Prevost LeMirage Liberty Coach
1984 TMC MC-9
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« Reply #7 on: November 13, 2009, 05:57:44 AM »

Was just a Top Sail Hill.just missed connection.would have came by.The Air system is very important (critical) so keep asking questions even if they sound dumb.....the dummist question is the one never ask.....what does your air gauges read on dash...Do they drop rapidly? Does your air drier blow off?
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Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana
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« Reply #8 on: November 13, 2009, 05:57:59 AM »

go to a fastenall store, they have the best 700 psi fittings at fair prices.and they have more selection than any other store in town.

Sorry, but I have to disagree with you here.  Use ONLY DOT approved fittings on your brake system.  They will be stamped DOT. They cost more than very similar brass fittings but are designed for the abuse a brake system takes.  Generally longer barrel for more support.  Be sure to use a brass ferrule inside the tubing.

You could probably use generic brass in the aux air systems (horn, wipers, suspension etc.) to save a buck,  but I wouldn't do it.  It's a one time expense, not a place to short change yourself.
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« Reply #9 on: November 13, 2009, 07:21:57 AM »

Brian, as has been noted you MUST only use DOT tubing and fittings!!!

I use these fittings and tubing on my system.  A really good source is McMaster Carr (http://www.mcmaster.com/#d.o.t.-tube-fittings/=4hhs6c).  They are a great company to deal with and their delivery is very fast.  I think their service is absolutely fantastic and prices seem fair. 

I believe that their fittings with pipe threads are coated with Teflon for sealing.

You can get the tubing (DOT Nylon) there as well.

From the above link you will see that there are two types of fittings:  compression and push-to-connect (""quick connect).  I believe that DOT now approves the push-to-connect fittings for all air brake connections.  They are much easier to use and let you avoid putting any twist in the tubing (think that might be the problem with your air bag hose).

The valve you are looking at is probably the relay valve.  They are not expensive and almost all are generic parts on buses.  They can also be rebuilt.

Jim
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Jim Shepherd
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« Reply #10 on: November 13, 2009, 11:19:50 AM »

The relay valve may be alright.  It may be dumping air coming from your rear brakes if one or both of the cans are bad.  That is definitely the place to start, but you should have it checked by someone the really knows what they are doing.  If they are springs brakes, the cans are cheap.  I thought that I had a bad relay valve when I got my bus.  Fortunately, when I called Luke to see about getting one, he told me what I have said above leading to an expensive, but thorough and mandatory brake system overhaul.
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« Reply #11 on: November 13, 2009, 11:40:57 AM »

Brian, you will find all approved DOT fitting and hoses at any decent hydraulic hose supply I live in the middle of nowhere and the hose  supply here always have the fittings and lines. 
The only part he will not have is a coupling to splice 2 lines together I guess that is a no-no now for DOT


good luck
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« Reply #12 on: November 13, 2009, 02:46:18 PM »

Isn't a coupler how air seats hook up for their air supply?
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Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
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« Reply #13 on: November 13, 2009, 02:51:51 PM »

Isn't a coupler how air seats hook up for their air supply?

Maybe so, but that's on the auxillary tank. I'm sure couplings are a no no, too much chance for failure and another spot for leakage. I don't like them myself, better off getting the correct length and be done with it. The DOT line is probably cheaper than the brass fitting.
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« Reply #14 on: November 13, 2009, 03:27:23 PM »

I can see folks wanting to take a shortcut and use a coupler instead of fishing new air line through a tight space.  Personally, I would do it right.
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Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
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